The invention relates to a very high-speed electrical switchgear apparatus having the function of a limiting circuit breaker.
In the document EP 0,309,311 a limiting circuit breaker is described with high-speed opening control of the contacts by Thomson effect, each pole-unit of which circuit breaker is equipped with a movable assembly having a movable main bridge forming a main circuit with a pair of stationary main contacts connected to current input terminal strips, and a movable arcing contact bridge forming, with a pair of stationary arcing contacts, an arcing circuit connected in parallel with the main circuit. A Thomson effect thrust means drives the movable assembly for opening of the main circuit and of the arcing circuit. A latching device holds the movable assembly in the open position against the bias of return springs tending to return the movable assembly to the closed position. A second Thomson effect thruster serves the purpose of unlatching the latching device.
All the circuit breaker openings, whether it be simple operations or openings on faults, are caused by the Thomson effect actuator which therefore has to be dimensioned for a very large number of cycles. The Thomson effect actuator drives the contacts over the whole opening travel. Furthermore, the Thomson effect actuator requires its own electric power supply and, in case of failure of the latter, there is no subsidiary means of operating the apparatus. Moreover, the apparatus thus designed is very specific with respect to low-voltage power circuit breakers of conventional design which constitute the vast majority of the range, so that its cost remains high. Finally, the openings and closings by means of the Thomson effect actuator are extremely snappy, regardless of the type of fault. The mechanism of the apparatus therefore suffers considerably during the opening and closing cycles.
To limit shocks, it has been proposed in the document FR 2,377,086 to subdivide the electric power storage means by capacitors providing the power supply for the Thomson effect actuator into two parts. In case of opening under normal conditions, only one of the two parts is used whereas in case of an electric fault, both the parts of the energy storage means are used, a greater power then being available.
To operate Thomson effect limiting circuit breakers, electric short-circuit detection processes are known supplying a short-circuit detection signal very quickly and very reliably enabling high-speed operation of an electromechanical relay performing unlatching of a mechanism of the circuit breaker. The document DE 3,642,136 describes such a detection process using a current intensity signal and a current intensity differential signal to make a very quick decision as to the existence of a short-circuit. Early short-circuit detection combined with the speed of reaction of the Thomson effect actuator gives the circuit breaker a high-performance limiting function enabling it to break almost infinite prospective currents. However, the limiting function is only achieved by tripping of the circuit breaker, so that it does not enhance down-line selectivity in a distribution panel.
Circuit breakers are moreover known opening whereof is achieved by a spring-loaded mechanism and having a very short response time when tripping occurs on a fault. It has notably been proposed, in the document EP 780,380 A1, to use the mechanical reaction arising from electrodynamic compensation of the compensated contact means to bring about automatic tripping. The opening pawl comprises disengageable actuating means causing self-unlatching of the latch in the presence of a short-circuit current exceeding a calibration threshold defined by a spring, said self-unlatching being commanded from a mechanical reaction generated by the electrodynamic compensation effect and causing very fast rotation of the latch to unlatch the opening pawl before the trip means operates. To further improve the above device, it has been proposed, in the document FR 2,781,921, to add thereto electromagnetic limiting means performing separation of the contact fingers to limit very strong currents pending opening of the mechanism. The circuit breaker obtained has very high performances, but separation of the contact fingers by electromagnetic reaction cannot take place before the current intensity has exceeded a limiting threshold.
The object of the invention is therefore to remedy the shortcomings of the state of the art so as to propose an extremely reliable, relatively compact, low-cost limiting circuit breaker with very high-speed opening, enabling separation of the contacts and a limiting effect to be achieved without the current intensity having exceeded a limiting threshold.
For this purpose, the object of the invention is to provide an electrical switchgear apparatus comprising:
a first contact connected to a first terminal strip for connection to an electric power circuit;
a cage movable between a closed position and an open position;
a second contact electrically connected to a second terminal strip for connection to the electric power circuit, the second contact being movable with respect to the cage between a contact position and a separated position, the second contact being in contact with the first contact when the cage is in the closed position and the second contact is in the contact position,
a drive mechanism of the apparatus movable between a closed position and an open position, comprising:
an energy storage spring loaded when the drive mechanism is in the closed position and unloading when moving the drive mechanism from the closed position to the open position;
an opening latch, locking the drive mechanism in the open position;
an electromechanical relay for operation of the opening latch;
a kinematic transmission system between the energy storage spring and the cage to drive the cage from the closed position to the open position when the drive mechanism moves from the closed position to the open position;
an electromechanical actuator comprising a movable assembly moving between a rest position and an active position and driving the second contact from the contact position to the separated position going from the rest position to the active position, when the cage is in the closed position.
The presence of a drive mechanism independent from the actuator first of all makes it possible to limit the number of operations that have to be performed by the high-speed actuator since certain of the openings will be able to be performed by actuating the mechanism latch. In addition, the actuator only has to supply the energy required for moving the second contact to the separated position. When opening is confirmed by an unlatching order of the opening latch, the mechanism drives the contact support to the open position which has the effect of separating the movable contact even further from the first contact. In other words, a part of the travel of the movable contact with respect to the stationary contact is performed by the opening spring of the mechanism. The dimensioning of the actuator and associated electronics is thereby greatly simplified.
The redundance of the opening functions in addition enables downrated operation when malfunctioning of the electric power supply or power electronics associated to the very high-speed actuator, or even of the actuator itself, occurs. In this case, the circuit breaker in fact acts as a conventional limiting circuit breaker. The global reliability of the breaking function of the apparatus is thereby improved.
Furthermore, in so far as closing is performed by the mechanism, it is possible in case of closing on a fault to achieve immediate separation of the contacts by means of the actuator.
Preferably the apparatus in addition comprises a contact pressure spring urging the second contact to the contact position when the second contact is near to the contact position.
According to a first embodiment, the contact pressure spring bears on the movable cage. According to an alternative embodiment, the contact pressure spring bears on a support of the apparatus, the second contact being connected to the cage by a kinematic link.
Advantageously, the drive mechanism comprises closing means to move the drive mechanism from the open position to the closed position, the kinematic transmission system driving the cage from the open position to the closed position when the drive mechanism moves from the open position to the closed position. The closing means comprise a closing spring which relaxes to move the mechanism from the open position to the closed position. The energy storage spring is then said to be an opening spring to distinguish it from the closing spring. The apparatus may be of the type wherein the energy necessary to load the opening spring is first of all stored in the closing spring, relaxation of the closing spring enabling the opening spring to be loaded. Alternatively, it may be of the type wherein the energy necessary to load the closing spring is first of all stored in the opening spring, relaxation of the opening spring enabling the closing spring to be loaded. According to another embodiment, a single spring can perform both closing and opening on a fault.
According to one embodiment, the apparatus in addition comprises a means for retaining the second contact in a retention position situated between the contact position and the separated position so long as the cage is in the closed position. These retention means enable holding in the retention position to be achieved, pending opening of the mechanism by the energy storage spring. Preferably the retention means includes an anti-return latch movable between a neutral position and an anti-return position and moving from the neutral position to the anti-return position when the second contact moves from the contact position to the separated position, the anti-return latch in the anti-return position locking the second contact in a locked position near to the separated position so long as the cage is in the closed position. Positive locking of the second contact is thus achieved, resulting in efficient latching even in the case where the second contact, thrust by the actuator, bounces on reaching the separated position. Alternatively, a bistable articulation mechanism between the second contact and the cage can be achieved by means of the contact pressure springs, so that when the second contact is near to the separated position, it is urged to the separated position by the contact pressure spring. Such a device does however present the shortcoming of being less reliable in the event of violent bouncing of the second contact in the separated position. A top end-of-travel stop able to absorb the kinetic energy of the second contact should then be provided for the second contact.
Preferably, the apparatus in addition comprises
an arc extinguishing chamber equipped with means for absorbing energy given off by an electric arc drawn between the first contact and the second contact when the second contact is separated from the first contact,
means for projecting an electric arc drawn between the first contact and the second contact by electromagnetic effect to the arc extinguishing chamber.
These means enable the energy of the electric arc to be absorbed as soon as the contacts are separated by the electromagnetic actuator, without waiting for confirmation of opening by the drive mechanism. Preferably, the chamber and the means for electromagnetic propulsion of the arc are dimensioned in such a way that the arc is extinguished even before the drive mechanism has been able to move the cage. In practice, projection of the arc to the chamber is obtained notably by giving the conductors connecting the contacts to the connection terminal strips a suitable shape, for example the shape of a current loop. A U-shaped magnetic circuit surrounding the contact zone can also be inserted to produce a strong electromagnetic field in the zone where the electric arc arises when separation of the contacts takes place.
Advantageously, the apparatus in addition comprises an electric power supply device to supply the electromechanical actuator and deliver the electric power required to make the movable assembly go from the rest position to the active position. The electric power supply device comprises an electric power storage means. In practice, this involves one or more power capacitors which enable electric power to be stored and restored almost instantaneously to supply power to the actuator. According to one embodiment, the electric power supply device is connected to an electric source independent from the electric power circuit. However, it can also be envisioned to provide a control whose electric power source is the electric power circuit wherein the contacts of the apparatus are situated.
The operating mechanism of the apparatus can be constructed according to different layouts. In the case of a circuit breaker, the following can be provided:
means for detecting electric faults and for discriminating between electric faults requiring high-speed opening and electric faults not requiring high-speed opening;
operating means to operate both the electromechanical relay and the electric power supply device when the means for detecting and discriminating have decided that the electric fault requires high-speed opening and to operate the electromechanical relay alone when the means for detecting and discriminating have decided that the electric fault does not require high-speed opening.
Alternatively the following can be provided:
measuring means for measuring an electric characteristic of the electric power circuit;
a trip device of the mechanism connected to the measuring means and to the electromechanical relay to operate the electromechanical relay;
a high-speed opening device connected to the measuring means and to the electric power supply device to operate the electromechanical actuator when the electric fault requires high-speed opening.
According to another alternative, the following are provided:
measuring means for measuring an electric characteristic of the electric power circuit;
a trip device of the mechanism connected to the measuring means and to the electromechanical relay to operate the electromechanical relay in response to the signal representative of an electric fault;
a high-speed opening device connected to the measuring means, to the electromechanical relay and to the electric power supply device, to operate both the electromechanical relay and the electromechanical actuator when the electric fault requires high-speed opening.
The latter solution provides an additional redundance at the level of control of the relay controlling opening of the mechanism.
According to another, preferred, alternative, the following are provided:
measuring means for measuring an electric characteristic of the electric power circuit;
a trip device of the mechanism connected to the measuring means and to the electromechanical relay to operate the electromechanical relay in response to the signal representative of an electric fault;
a high-speed opening device connected to the measuring means, to the trip device and to the electric power supply device, to operate both the electromechanical relay and the electromechanical actuator when the electric fault requires high-speed opening.
This solution in all cases enables opening of the relay to be commanded by means of the trip device, but specific tripping conditions of the relay to be imposed in the case where opening of the mechanism is preceded by separation of the contacts by the electromechanical actuator.
In a preferred practical application, the measuring means are formed by Rogowsky coils.
The electromechanical actuator is preferably constituted by a Thomson effect thruster. Any other very high-speed electromechanical thruster can naturally be envisioned.